N‐Methylation of N‐Methylaniline with Carbon Dioxide and Molecular Hydrogen over a Heterogeneous Non‐Noble Metal Cu/TiO2 Catalyst

Abstract A non‐noble heterogeneous catalyst of Cu/TiO 2 was prepared for N ‐methylation of N ‐methylaniline (MA) with CO 2 and H 2 . 5 wt.–% Cu loaded TiO 2 (P25) catalyst exhibited a high performance, with 82 % MA conversion and 98 % N,N ‐dimethylaniline (DMA) selectivity under the reaction conditions used (4 MPa H 2 , 2 MPa CO 2 , 180 °C, 36 h). The Cu/TiO 2 catalyst was more effective with respective to the total conversion and the DMA selectivity as compared to 5 wt.–% Cu loaded catalysts on CeO 2 , ZnO and activated carbon materials. The possible active species of Cu/TiO 2 catalyst should be both Cu + and Cu 0 which contributed to the high activity as the reaction conversion increased linearly with them exposed on the surface of catalyst. Moreover, the reaction pathways involved were studied; it was likely that the reaction took place via an intermediate of formaldehyde that was formed from CO 2 and H 2 , as confirmed by in situ diffuse reflectance Fourier‐transform infrared spectroscopy, then it reacted with MA to give N ‐methylformanilide (MFA), and finally MFA was hydrogenated to DMA.